1. Field of the Invention
This Application relates to a catalyst for high purification of exhaust gases of internal combustion engines and of industry, mainly from carbon monoxide and organic compounds which catalyst is free of platinum and/or palladium and rhodium and other precious and rare metals and has an excellent converting activity at moderate temperatures and limit-level of thermostability not lower than 1000.degree. C. This Application is a Continuation-In-Part Application of our earlier U.S. patent application Ser. No. 08/676,585 now abandoned, which is incorporated herein by reference, in its entirety.
2. Description of the Prior Art
Transition metal oxides show catalytic activity in the processes of deep oxidation of carbon monoxide and organic compounds. The most active among them are complex metal oxide structures named perovskites and spinels which are potentially competitive towards well known catalysts containing precious metals.
Thus complex oxides catalyst with perovskite structure was disclosed in patent literature represented by general formula Ln.sub.1-x A.sub.x MO.sub.3, wherein Ln is at least one rare earth metal. "A" is alkaline earth metal, and "M" represents at least one transition element and "X" varies in range O&lt;X&lt;1. These catalysts have been expected to be put into practical use as an inexpensive 3-way catalysts for converting carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO.sub.x). However, they can be used only at temperature below 800.degree. C. and are therefore unsatisfactory as catalyst for automobile exhaust gases because such catalysts are required to have a high catalytic activity and durability in a temperature range as high but not lower than 900.degree. C. It is to be noted also, that neither low temperature activity nor stability to poisoning is claimed at all for Ln.sub.1-x A.sub.x MO.sub.3.
Good activity and resistance to high temperatures up to 1050.degree. C. were also maintained for the catalyst for treating exhaust gas from vehicle engines which comprises a sintered substance composed of ferric oxide and at least one other metallic oxide of the group consisting of copper, manganese, and chromium oxide and forming at least in part a spinel crystal structure. These catalytic sintered masses may also include aluminum oxide as reinforcing agent and other additives, such as MgO, CaO, SiO.sub.2, V.sub.2 O.sub.5, NiO, Co.sub.3 O.sub.4, ZnO, Ce, Sb, Co, Ti, K, Ag, W.
However, this catalyst cannot be said to be satisfactory in practical use because of its insufficient activity. The temperatures corresponding to complete carbon monoxide (CO) and hydrocarbon (CH) oxidation on this catalyst are markedly above about 300.degree. C. This catalysts' imperfection is caused mainly by two factors. The first of them is due to the process for catalyst manufacturing, i.e. high temperature sintering of individual oxide mixtures. In the consequence of this procedure catalyst particles have very low surface area. This shortcoming seriously restricts catalyst productivity in oxidation process. The second factor which causes catalyst inadequate activity is due to some limitations of its composition and structure. This conclusion implies that oxide ratios in starting mixtures are those forming at least in part a spinel crystal structure in the course of sintering. Thus, sintered catalytic mass is essentially heterogeneous, i.e. contains in part a catalytically active spinel structure along with several moderately active and inactive individual metal oxides that reduce catalysts productivity in CO and CH oxidation processes.
Binary oxide spinel structures of the formula MA1.sub.2 O.sub.4 wherein "M" is Cu, Mn, Mo, Zn, Fe, Co, Ni or Sr are also known in the art as materials for carrier coating in manufacturing of supported Pt, Pd-containing catalysts useful in the purification of exhaust gases. The function of this spinel-containing coating is to improve Pt(Pd)-catalysts durability and service life. However, it seems to the present inventors that this coating composition, as well as the method of its deposition onto the carrier can be improved. The principal limitation is that said spinel is used in a form of sintered particles and therefore cannot form continuous film on a carrier surface. Besides that, there is a simple binary composition of said spinel which reduces its adhesion as well as its long-term maintenance of support thereon as an active form.